Gets highest combination possible from a positive integer array

highestCombination.js

const arr = [9, 90, 95, 99, 50, 5, 56, 504, 5006, 544, 1]

const highestCombination = (a) => {
  const grouped = a.reduce(
    (acc, c) => {
      const cInitial = `${c}`.split('')[0]
      acc[cInitial] ?
        acc[cInitial].items.push(c)
        :
        acc[cInitial] = { items: [c], longest: 0 }
      acc[cInitial].longest = acc[cInitial].longest > `${c}`.length ? acc[cInitial].longest : `${c}`.length
      return acc
    },
    {}
  )

  const getAbsVal = (n, long) => {
    const str = `${n}`
    const splitted = str.split('')
    const toRepeat = splitted[str.length - 1] > splitted[0] ? splitted[str.length - 1] : splitted[0]
    return str + toRepeat.repeat(long - str.length)
  }

  return Object.keys(grouped)
    .sort((a, b) => a < b)
    .reduce(
      (acc, key) => {
        const items = grouped[key].items.sort((a, b) => {
          const A = getAbsVal(a, grouped[key].longest)
          const B = getAbsVal(b, grouped[key].longest)
          return parseInt(A, 10) < parseInt(B, 10)
        })
        return [...acc, ...items]
      },
      []
    )
    .join('')
}

console.log(highestCombination(arr))